1998 Land Rover Freelander Freelander problems-coolant

Engine Cooling problem
1998 Land Rover Freelander Four Wheel Drive Manual 101000 miles

Hello,
I recently purchased a 98 freelander with K series engine, I understand they have there problems but I am the type of person who likes to maintain the engine. My problem is firstly I noticed my coolant had turned a Brown colour, upon further inspection it was quite sludgy so I cleaned what I could from the header tank and topped up my blue coolant/water. More recently the coolant level keeps going down and needs topping up regulary ( still a little merky). I can not see any leaks on any of the hoses or header tank, one of the hoses had just been replaced when I puchased the Vehicle, I have noticed that the fans have not been active but not sure when they are supposed to be.
Also the Hill decent light remains on and will not go out.
Sunroof makes a noise as if its going to open but does not move.
Any help with the above will be appreciated.